Extremism means, literally, "the quality or state of being extreme" or the "advocacy of extreme measures or views".[1]

Nowadays, the term is mostly used in a political or religious sense, to refer to an ideology that is considered (by the speaker or by some implied shared social consensus) to be far outside the (acceptable) mainstream attitudes of society,[2] but extremism can, for example, also be meant in an economic sense.

The term "extremism" is usually meant to be pejorative; that is, to express (strong) disapproval. However, it may also be used in a more academic, purely descriptive, non-condemning sense.

They have been many different definitions of "extremism". Peter T. Coleman and Andrea Bartoli give observation of definitions:[4] Extremism is a complex phenomenon, although its complexity is often hard to see. Most simply, it can be defined as activities (beliefs, attitudes, feelings, actions, strategies) of a character far removed from the ordinary. In conflict settings it manifests as a severe form of conflict engagement. However, the labeling of activities, people, and groups as "extremist", and the defining of what is "ordinary" in any setting is always a subjective and political matter. Thus, we suggest that any discussion of extremism be mindful of the following: Typically, the same extremist act will be viewed by some as just and moral (such as pro-social "freedom fighting"), and by others as unjust and immoral (antisocial "terrorism") depending on the observer's values, politics, moral scope, and the nature of their relationship with the actor. In addition, one's sense of the moral or immoral nature of a given act of extremism (such as Nelson Mandela's use of guerilla war tactics against the South African Government) may change as conditions (leadership, world opinion, crises, historical accounts, etc.) change. Thus, the current and historical context of extremist acts shapes our view of them. Power differences also matter when defining extremism. When in conflict, the activities of members of low power groups tend to be viewed as more extreme than similar activities committed by members of groups advocating the status quo.

In addition, extreme acts are more likely to be employed by marginalized people and groups who view more normative forms of conflict engagement as blocked for them or biased. However, dominant groups also commonly employ extreme activities (such as governmental sanctioning of violent paramilitary groups or the attack in Waco by the FBI in the U.S.). *Extremist acts often employ violent means, although extremist groups will differ in their preference for violent vs. non-violent tactics, in the level of violence they employ, and in the preferred targets of their violence (from infrastructure to military personnel to civilians to children). Again, low power groups are more likely to employ direct, episodic forms of violence (such as suicide bombings), whereas dominant groups tend to be associated with more structural or institutionalized forms (like the covert use of torture or the informal sanctioning of police brutality).[4]

Although extremist individuals and groups (such as Hamas and Islamic Jihad) are often viewed as cohesive and consistently evil, it is important to recognize that they may be conflicted or ambivalent psychologically as individuals, or contain difference and conflict within their groups. For instance, individual members of Hamas may differ considerably in their willingness to negotiate their differences with the Palestinian Authority and, ultimately, with certain factions in Israel. Ultimately, the core problem that extremism presents in situations of protracted conflict is less the severity of the activities (although violence, trauma, and escalation are obvious concerns) but more so the closed, fixed, and intolerant nature of extremist attitudes, and their subsequent imperviousness to change.[4]

Eric Hoffer and Arthur Schlesinger, Jr. were two political writers during the mid-20th century who gave what purported to be accounts of "political extremism". Hoffer wrote books such as The True Believer and The Passionate State of Mind about the psychology and sociology of those who join "fanatical" mass movements. Schlesinger wrote books such as The Vital Center, championing a supposed "center" of politics within which "mainstream" political discourse takes place, and underscoring the alleged need for societies to draw definite lines regarding what falls outside of this acceptability.

Seymour Martin Lipset argued that besides the extremism of the left and right there is also an extremism of the center, and that it actually formed the base of fascism.[5]

Joining extremist groups has been seen to arise from beliefs about the acceptability of aggression towards the group's target. For example, in Pakistan, beliefs about the acceptability of aggression against Jews were shown to predict who would join an extremist anti-Semitic group.[7] Cultural differences in acceptability about aggression towards certain groups may explain extremism towards certain targets, and as these beliefs can be easily changed through intervention, this may offer a way in which extremism can be discouraged.[7]

"Extremism" is not a stand-alone characteristic. The attitude or behavior of an "extremist" may be represented as part of a spectrum which ranges from mild interest through "obsession" to "fanaticism" and "extremism". The alleged similarity between the "extreme left" and "extreme right", or perhaps between different religious "zealots", may mean only that all these are "unacceptable" from the standpoint of a supposed mainstream or majority.

Economist Ronald Wintrobe[8] argues that many extremist movements, even though having completely different ideologies share a common set of characteristics. As an example, he lists the following common characteristics between "Jewish fundamentalists" and "the extremists of Hamas":[9]

Among the explanations for extremism is one that views it as a plague.[4]Arno Gruen said, "The lack of identity associated with extremists is the result of self-destructive self-hatred that leads to feelings of revenge toward life itself, and a compulsion to kill one's own humanness." Thus extremism is seen as not a tactic, nor an ideology, but as a pathological illness which feeds on the destruction of life.[4]Dr. Kathleen Taylor believes religious fundamentalism is a mental illness and that is "curable."[10]

Another view is that extremism is an emotional outlet for severe feelings stemming from "persistent experiences of oppression, insecurity, humiliation, resentment, loss, and rage" which are presumed to "lead individuals and groups to adopt conflict engagement strategies which "fit" or feel consistent with these experiences".[4]

Extremism is however seen by other researchers as a "rational strategy in a game over power".[4] See for instance the works of Eli Berman.

Robert F. Kennedy said "What is objectionable, what is dangerous about extremists is not that they are extreme but that they are intolerant. The evil is not what they say about their cause, but what they say about their opponents."

In Russia, the laws prohibiting extremist content are used (both by poorly trained officials and as part of an intentional politics to suppress opposition) to suppress the freedom of speech through very broad and flexible interpretation.[11] Publications classified as "extremist" and thus prosecuted included protests against the court rulings in Bolotnaya Square case ("calling for illegal action"), criticism of overspending of local governor ("insult of the authorities"), publishing a poem in support of Ukraine ("inciting hatred"),[12][13] an open letter against a war in Chechnya by a writer Polina Zherebcova,[14] the whole Jehovah's Witnesses movement in Russia,[15]Raphael Lemkin, and articles by initiator of the Genocide Convention of 1948.[16]